This series consists of talks in the area of Superstring Theory.
Motivated by recent mathematical developements in non-commutative Donaldson-Thomas theory, we construct a new statistical mechanicalmodel of crystal melting to count BPS bound states of D0 and D2 branes on a single D6 brane wrapping an arbitrary toric Calabi-Yau threefold. We also discuss the wall crossing phenomena, which are crucial for the proper understanding of the relation between the crystal melting and the topological string theory.
We derive a universal upper bound on the weight of the lowest primary operator in any two-dimensional conformal field theory with a given central charge. Translated into gravitational language using the AdS/CFT dictionary, our result proves rigorously that the lightest massive state in any theory of 3D gravity and matter with negative cosmological constant can be no heavier than a particular function the cosmological constant and the Planck scale. For a large AdS space, the lower bound approaches the mass of the lightest BTZ black hole.
In the past couple of years many new developments have been made in the techniques used for computing one-loop gauge theory amplitudes. These developments have mainly involved exploiting generalized unitarity techniques to construct the coefficients of the basis integral functions which make up a one-loop amplitude. I will outline these new developments along with their application to both QCD and N=8 supergravity amplitudes.
In this talk I discuss methods to determine hydrodynamical dispersion relations from an extra-dimensional gravity dual wherein the metric is supported by scalar fields. Such a setup may eventually be used as a model of the strongly coupled plasma created in heavy ion collisions. I examine examples of both the shear and sound modes. The shear mode is analyzed using the black hole membrane paradigm; a calculation of the shear viscosity is reviewed, and then the calculation is extended to the next hydrodynamical order. All results agree with those found using the AdS/CFT prescription.
Understanding dynamics of strongly coupled quantum field theories is an important problem in both condensed matter physics and high energy physics. In condensed matter systems, interacting quantum field theories can arise either at a critical point, or in a finite region of a parameter space. In the former case, massless modes arise as a result of fine tuning of external parameters, while, in the latter case, massless modes are protected by topology and/or symmetry.
We discuss various properties of holographic mesons in a deconfined strongly coupled plasma. We show that such mesons obtain a width from a non-perturbative effect. On the string theory side this is due to open string modes on a D-brane tunneling into a black hole through worldsheet instantons. On the field theory side these instantons have the simple interpretation as heavy thermal quarks. We also comment on how this non-perturbative effect has important consequences for the phase structure of the Yang-Mills theory obtained in the classical gravity limit.
We discuss holography for geometries that are asymptotic to non-conformal brane backgrounds. The near-horizon limit of all non-conformal branes, including D-branes and the fundamental string but excluding five-branes, is conformal to $AdS_{p+2} imes S^{8-p}$ with a linear dilaton. They exhibit a generalized conformal structure, both on the QFT and on the gravitational side. We develop holographic renormalization for all these cases and discuss a number of applications.
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